In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations, including polishing, buffing, and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. As is well known, patterned conductive circuit layers are insulated from other conductive layers by a substrate, such as silicon dioxide. Without planarization, fabrication of additional layers becomes substantially more difficult due to higher variations in the surface topography.
In prior art CMP systems, the wafers are scrubbed, buffed and polished on one or both sides. Such systems typically implement belts, pads or brushes to assist in the removal and polishing of the wafer surface. A colloid, usually a slurry, is often used to assist in the polishing process. The slurry is applied to a moving surface such as a belt, pad, brush or the like to aid in the removal of material from a wafer surface in order to achieve a flat surface. The slurry also acts as a carrier to remove the particles removed from the wafer surface.
In linear planarization technology, a rotating head carries a wafer and the surface of the wafer is applied to a moving linear belt that includes a layer of slurry. As the rotating wafer is applied to the surface of the belt, a force is applied to the opposing surface of the belt to control the wear rate of the wafer. In general, the wear rate is a function of the belt velocity and force applied to the wafer by the wafer carrier. The wear rate during the planarization process is variable and dependent upon the pressure applied to the opposing sides of the linear belt. Typically, a fluid bearing is utilized to apply an equal and opposite force to the linear belt to oppose the force applied by the wafer carrier and wafer to the linear belt.
The fluid bearing creates a thin film, or cushion, of pressurized fluid to support a load, similar to the technology used in air hockey tables. In the linear planarization technology, the air bearing counteracts the downward force from the semiconductor wafer onto the linear belt. The typical linear planarization system employs a hydrostatic air bearing, similar to the fluid bearing described in U.S. Pat. No. 5,916,012 entitled “Control of Chemical-Mechanical Polishing Rate Across a Substrate Surface for a Linear Polisher.” A hydrostatic air bearing is created by the flow of pressurized air through small gas jets. Generally, multiple airjet inlet holes are located in the form of circular rings about the center of a platen, and each of the rings of air-jets is controlled by regulating the pressure of the air supply to each ring. Such control is accomplished by using a multitude of pressure regulators and also requires a large supply of clean dry air. The air consumption of the hydrostatic air bearing incorporated into the linear planarization method is several times larger than that required by comparative techniques such as rotary and orbital methods. The large amount of air consumption necessary with hydrostatic air bearings in linear planarization technology can add cost and complexity to a polishing system.